This invention relates to a method for protecting titanium and titanium alloy elements. More particularly, this invention concerns itself with the use of copper shims for the prevention of fretting fatigue of titanium alloys.
The present interest in the use of aircraft gas turbine engines has created a need for the development of treatments which can alleviate excessive wear on engine components. Many of these components are fabricated from titanium and its alloys. Unfortunately, these alloys are susceptible to excessive wear during the periods of stress and strain encountered within the turbine engine's operational environment.
One form of wear which is especially severe is fretting. It is a form of wear indigenous to the mating surfaces of bolted flanges. In a gas turbine engine, the bolted flanges of compressor disks, or disks and stub shafts, or blade dovetail pressure faces are typical examples of potential sites for fretting fatigue. It is caused by the very small relative motion due to differential strain in the mated surfaces associated with the stresses of engine operation. Surface damage from fretting eventually creates stress raisers which, in the presence of otherwise normal and acceptable states-of-stress, can cause unexpected fatigue failure. Titanium and its alloys are naturally sensitive to surface conditioning, and their beneficial characteristics are substantially deteriorated by fretting.
With the present invention, however, it has been found that fretting fatigue in titanium and titanium alloy engine components can be minimized effectively and their fatigue life enhanced by utilizing thin copper shims placed between the mating surfaces of the titanium engine components.